Evaluating Seals: Determining the Hydrocarbon Retention Potential of Caprocks


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The accumulation of hydrocarbons requires a porous reservoir overlain by an impermeable caprock or seal. The importance of the caprock is that it provides containment of buoyant hydrocarbon. Determining which seals have the potential to trap economically viable hydrocarbon accumulations, versus those that hold sub-economic volumes, has become an important aspect of evaluating both basin-wide petroleum systems and field scale prospects. Reducing the uncertainties associated with the evaluation of seals can be done by understanding the seal potential of the seal. Seal potential is defined as the 1) seal capacity, 2) seal geometry and 3) seal integrity of the caprock. Seal capacity refers to the hydrocarbon column height that the caprock can retain before capillary forces allow the migration of the hydrocarbon into and possibly through the caprock. Seal geometry refers to the thickness and lateral extent of the caprock. The caprock must have sufficient lateral extent to cover whatever structural, or stratigraphic trap is trapping the hydrocarbon accumulation. In addition, it must be thick enough to maintain an effective seal across any faults that displace it. Seal integrity refers to geomechanical properties of the caprock. These properties, controlled by lithology, thickness, ductility and fracture density, are determined by microscopic and macroscopic analyses of the caprock and analyses of regional, local and possible induced stress fields. Case studies from the Gulf of Papua and offshore northwest Java demonstrate the application of seal potential methodology. In a more topical sense, determining the viability of caprocks for the retention of CO2 is a critical element in the selection of sites for safe CO2 injection and secure storage in commercial scale carbon capture and storage (CCS) projects.

Your Instructor

John Kaldi, PhD, PESA
John Kaldi, PhD, PESA

John Kaldi is an Emeritus Professor of Petroleum Geology and Engineering at the Australian School of Petroleum and Energy Resources (ASPER), University of Adelaide, is a CO2CRC Distinguished Scientist and holds the South Australia State Chair in Carbon Capture & Storage (CCS). He is also an Adjunct Professor at Institut Teknologi Bandung (ITB), Indonesia, and a Visiting Professor at Universiti Teknologi Petronas (UTP) in Malaysia. John received his Bachelors and Master’s degrees in geology from Queens College, City University of New York, and a PhD in Geology from Cambridge University in the UK. His career includes 18 years in the Petroleum Industry in both technical and managerial roles with Shell, Arco & Vico. John served as Distinguished Lecturer for various professional organisations, including SPE, AAPG, the Indonesian Petroleum Association (IPA) and the Petroleum Exploration Association of Australia (PESA). He has been the author and presenter of over 150 journal articles and technical conference papers.

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